Aggregation over different qualities: Are there generic commodities?

Aggregation over goods is always an issue in empirical analysis. However, while the problem of aggregation over different goo s often is analysed, little attention has been given to the properties of generic goods such as e.g. coffee, wheat and salmon.Often these generic commodities contain a number of different qualities. In this paper a test for aggregation based on Lewbel 8217;s Generalized Composite Commodity Theorem (GCCT) using only price data is used to validate aggregation. We show by usingprice series for different weight-classes of salmon that the generic term salmon can be used for these products.